I am looking for a upgrade from my kit lens to a lens with much more potential, a lens that would be an all-rounder for me.

After some research I ended up with these two in the final list:

Canon EF-S 15-85 f3.5/5.6 IS USM and Canon EF 24-105 IS USM f4 L

My question is have any of you tried these two and what are your results with them?

Does the small price difference make sense in buying the L lens over the non L?

Is there a big difference in sharpness between them?

How do they cope with chromatic aberration?

As both have USM focusing I don't think there would be a difference in focusing speeds. The min-range and max-range difference is negligible in my situation as I shoot mostly portraits so I wouldn't be using the 15mm or 24mm end too often.

7 Answers
7

I own both lenses. I can't imagine the price difference between them being "small". So I just looked, $700 vs $1100... Both new, from reputable vendors. I wonder therefore if we are talking about the same glass.

As with any two lenses, there are pros and cons to each, off the top of my head, here's what I would say for each:

EF 24-105 f/4 L
Pros:

razor sharp

constant f/4 all the way from 24 to 105

fast auto focus, all the way out to 105, due to the constant f/4

well understood lens, supported by lots of correction software

minimal distortion, easily corrected

weather sealed, better construction

Cons:

heavy

bigger

needs bigger, more expensive filters

expensive

EF-S 15-85:
Pros:

cheaper

smaller

lighter weight

Cons:

can only be used with an aps-c body, if you ever want to move up to a full frame body down the road, you won't be able to use this lens.

the CA is pretty bad

as a less prevalent lens, especially in the pro space, the correction maps for it aren't as smooth as other lenses. If you are at one end or the other they are solid, if you were somewhere in the middle... They seem to just approximate it, leaving kinda less than stellar or consistent results.

variable max aperture

slower autofocus on most bodies, and progressively slower as you zoom in and the max aperture opens up.

Now, you say you are doing mostly portraits with this lens, so you won't be using the extreme ends of the zoom capacity. The 105 end of the 24-105 is a magnificent portrait lens, and being able to stay stopped down to f/4 at that end is a wonderful thing for shooting people. (That just never sounds right.)

You are buying a screwdriver for a nail

You shoot mostly portraits. You don't want a general purpose lens. Your idea of looking at these two lenses is in trouble from the start. You would be much much better suited to buy a wide prime and not a variable aperture f/3.5-4 lens. f/4 at 40mm is not a portrait lens.

I would look at the below question and buy a portrait lens and not a general purpose zoom.

Format is important

This question originally noted that you have a 60D APS-C camera. If you are going to buy a general purpose zoom, I would HIGHLY recommend buying the one that is better suited for your format. It sounds like you are moving from a 18-55mm kit lens. Do you only use that kit lens from 38-55mm? That is going to be similar to the new wide capabilities of the 24-105mm lens. That is a huge thing to give up, any shots wider then an effective focal length of 38mm. I would never consider or recommend the 24-105mm L lens for an APS-C sensor. It is a great lens on full frame, it is a non starter as far as I am concerned on an APS-C sensor. This is an opinion, but I feel strongly about it.

If you have a crop sensor body, I think you'll find that the 15mm side is a lot more useful than stopping only at 24mm. The "normal equivalent" on an APS-C is about 31mm, so 24mm is not that wide-angle.

Do you use a good post-processing program such as Lightroom? If so, most of the CA can be fixed in post using its lens-correction module.

I've got the EFS 17-55 F2.8, and not your two candidates. But I can warn you that many inexpensive Canon F3.5-5.6 zooms do not stay at F3.5 or even F4 for much of their range. They tend to quickly close down to F5.6. So you could be looking at a full stop for much of your real world shooting.

Looking at the fact that the 24-105 is a fixed aperture lens where as 15-85 is a variable aperture lens - since you say you would shoot mostly portraits, let's assume at 50mm on a crop body, according to this source the 15-85 will have a maximum aperture of around F/5.6, so that will give you a little deeper DOF than the F/4 for the 24-105 (IMHO, the 24-105 wins here by a small margin).

There are some good comparisons between the two lenses, like the ones on Flickr, POTN, and then some more. I wouldn't say all of these are relevant to you, since most of these comparisons also consider the wide and telephoto ends, which as you said, is not a big deal (although I would still consider that fact if that is my only lens - this, again, might not apply to you). But, if you have time, go through those links - they do have some useful information.

Looking at the excerpts, most people say the 24-105 is a tad sharper, although the 15-85 is not a sour looser. Coming to the chromatic aberrations, as Pat suggested, they are easy to be corrected in post processing.

As an all-around lens, I would go with the 15-85 if I don't have a lens that already doesn't cover the wider range. Otherwise, go with the 24-105 since that will also give you a wider aperture at longer focal lengths.

If I had Canon and portraits were my first priority, I would go for the 24-105 instead of 15-85 without any hesitation. it may be more expensive, but it's a great lens and a good investment in case you decided to upgrade to a Full Frame (such as 5D-x or 6D) latter.

I always recommend the Photozone.de website for lens review, you can find a lot of useful information there and IMO there is no use in posting them here again:

I was bitten by the "Oh I'll go to FF and ebay my 50d+lens and it'll be easy!"
Not so much. I struggled to sell it, and in the end gave up. I wasn't going to "give away" my old friend (the 15-85) that had served me well for many years.

So instead, I rented it out to a friend till October.

Anyway, long story short, if you might one day upgrade to FF, keep away from EF-S

True, I might and I was thinking about that and I'm still taking that into consideration and slightly tilting towards the EF lens. Although FF would bring some benefits, I don't think it's lower noise performance is enough of a strong point. Apart from noise performance I don't see why I'd go FF.
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Radu GheorghiuFeb 6 '13 at 11:54